The present invention relates in general to a rotary speed regulating system, particularly for regulating the idling speed of an internal combustion engine. The system includes a generator for producing a desired-value signal, a sensor for sensing the actual speed value, a regulator responsive to the desired and actual speed values, and a fuel mixture adjuster responsive to the output signal from the regulator.
Arrangements are known from prior art which regulate the rotary speed of internal combustion engines, especially in motor vehicles. Of particular interest are the arrangements for regulating the no-load or idling speed of the engine, because if a motor vehicle is equipped with connectable and disconnectable consumers then, when the engine is idling, a strong reduction of its rotary speed, or even a stoppage, may occur when such a consumer is suddenly switched on. For example, when in a standing motor vehicle with running motor an air conditioner, or an automatic shifting device, or a power steering device, or the like, is suddenly activated, the aforementioned drop in the rotary speed will take place. In an unregulated IC engine, the total load may be so large that the engine stalls. In addition, in the endeavor to save energy it is desirable to set the engine for lowest idling speed. A no-load speed regulation of this kind is therefore of importance, both for fitting up the engine and for special operation conditions such as for idling speeds and the like.
For regulating idling speeds, it has been known to employ conventional P-, PI- or PID-regulators. In those regulators, the operation is based generally on the detection of the deviation of the actual rotary speed of the engine from the desired one. Such a known arrangement is described, for example, in U.S. Pat. No. 3,661,131. The disadvantage of such prior-art speed regulators is in a relatively slow response, because the rotary speed increase or decrease is the last effect of varying operational conditions. As a consequence, the prior-art regulating systems cannot distinguish different operational conditions. For example, a conventional speed regulator cannot distinguish whether a motor vehicle is stationary during idling or whether it slowly moves. In the latter case, the regulator permits the speed drop up to a zero value, so that a fuel mixture adjuster, usually a bypass valve associated with a throttle valve, is completely closed. Due to the relatively high rotary speed of the engine during the slow pull-up movement of the motor vehicle, the fuel mixture in the intake manifold is completely sucked up by the engine. If the operator during this pull-up operation steps on the clutch and if a larger consumer, such as an air conditioner is on, then in spite of immediate opening of the fuel mixture adjuster the dynamic behavior of the rotary speed regulation has hardly any effect, inasmuch as the intake pipe or manifold must first be filled up. This delay is manifested in a strong subharmonic oscillation of the course of the rotary speed, which under certain circumstances may lead to stalling of the engine when it falls below its running limit. Under this particular operational condition, a conventional idling speed regulation of the engine is proved as disadvantageous in comparison with unregulated engines, inasmuch as in the latter case always a certain amount of residual air is supplied through the idling speed setting propeller, and the intake manifold is not completely empty. This aforementioned disadvantageous operational condition of the idling internal combustion engine may occur also in motor vehicles with automatic transmissions when a vehicle during its slow pull-up movement is suddenly braked. In this case a reverse shift is introduced in the gear control, due to the sinking speed of movement, and a positive coupling between the engine and the gears is momentarily interrupted.
From the publication WO-A1-81/01591, it is known how to employ the suction pressure of the internal combustion engine for regulating its idling speed. This known device, however, employs the suction pressure only, and consequently an exact maintenance of the idling speed is not guaranteed, and especially a predetermined desired value of the rotary speed cannot be obtained.